<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Element对象</title>
</head>
<body>
    <a>点我试一试</a>
    <input id="btn_set" type="button" value="设置属性">
    <input id="btn_remove" type="button" value="删除属性">


    <script>
      //获取 btn
      var btn_set = document.getElementById("btn_set");
      btn_set.onclick = function () {
        //1.获取 a 标签
        var element_a = document.getElementsByTagName("a")[0];
        element_a.setAttribute("href","http://www.baidu.com");
      }

      //获取 btn
      var btn_remove = document.getElementById("btn_remove");
      btn_remove.onclick = function () {
        //1.获取 a 标签
        var element_a = document.getElementsByTagName("a")[0];
        element_a.removeAttribute("href");
      }

    </script>
</body>
</html>